Optimizing Autotrophic Sulfide Oxidation in the Oxygen-Based Membrane Biofilm Reactor to Recover Elemental Sulfur.

Biological sulfide oxidation is an efficient means to recover elemental sulfur (S0) as a valuable resource from sulfide-bearing wastewater. This work evaluated the autotrophic sulfide oxidation to S0 in the O2-based membrane biofilm reactor (O2-MBfR). High recovery of S0 (80-90% of influent S) and high sulfide oxidation (∼100%) were simultaneously achieved when the ratio of O2-delivery capacity to sulfide-to S0 surface loading (SL) (O2/S2- → S0 ratio) was around 1.5 (g O2/m2-day/g O2/m2-day). On average, most of the produced S0 was recovered in the MBfR effluent, although the biofilm could be a source or sink for S0. Shallow metagenomic analysis of the biofilm showed that the top sulfide-oxidizing genera present in all stages were Thauera, Thiomonas, Thauera_A, and Pseudomonas. Thiomonas or Pseudomonas was the most important genus in stages that produced almost only S0 (i.e., the O2/S2- → S0 ratio around 1.5 g of the O2/m2-day/g O2/m2-day). With a lower sulfide SL, the S0-producing genes were sqr and fccAB in Thiomonas. With a higher sulfide SL, the S0-producing genes were in the soxABDXYZ system in Pseudomonas. Thus, the biofilm community of the O2-MBfR adapted to different sulfide-to-S0 SLs and corresponding O2-delivery capacities. The results illustrate the potential for S0 recovery using the O2-MBfR.

Elemental sulfur biorecovery from phosphogypsum using oxygen-membrane biofilm reactor: Bioreactor parameters optimization, metagenomic analysis and metabolic prediction of the biofilm activity.

This work investigated elemental sulfur (S0) biorecovery from Phosphogypsum (PG) using sulfur-oxidizing bacteria in an O2-based membrane biofilm reactor (MBfR). The system was first optimized using synthetic sulfide medium (SSM) as influent, then switched to biogenic sulfide medium (BSM) generated by biological reduction of PG alkaline leachate. The results using SSM had high sulfide-oxidation efficiency (98 %), sulfide to S0 conversion (∼90 %), and S0 production rate up to 2.7 g S0/(m2.d), when the O2/S ratio was ∼0.5 g O2/g S. With the BSM influent, the system maintained high sulfide-to-S0 conversion rate (97 %), and S0-production rate of 1.6 g S0/(m2.d). Metagenomic analysis revealed that Thauera was the dominant genus in SSM and BSM biofilms. Furthermore, influent composition affected the bacterial community structure and abundances of functional microbial sulfur genes, modifying the sulfur-transformation pathways in the biofilms. Overall, this work shows promise for O2-MBfR usage in S0 biorecovery from PG-leachate and other sulfidogenic effluents.

Effect of alkaline leaching of phosphogypsum on sulfate reduction activity and bacterial community composition using different sources of anaerobic microbial inoculum.

Phosphogypsum (PG), a by-product of the phosphate industry, is high in sulfate, (SO42-), which makes it an excellent substrate for sulfate-reducing bacteria (SRB) to produce hydrogen sulfide. This work aimed to optimize SO42- leaching from PG to achieve a high biological reduction of SO42- and generate high sulfide concentrations for subsequent use in the biological recovery of elemental sulfur. Five SRB consortia were isolated and enriched from: IS (Industrial sludges), MS (Marine sediments), WC (Winogradsky column), SNV (petroleum industry sediments) and PG (stored Phosphogypsum). The five consortia showed reduction activity when using PG leachate (with water) as source of SO42- and lactate, acetate, or glucose as the electron donor. The highest reduction rate (81.5 %) was registered using lactate and the IS consortium (81.5 %) followed by MS (79 %) and PG (71 %). To enhance the concentration of leached SO42- from PG for future utilization with the isolated consortia, PG was treated with NaOH solutions (2 % and 5 %). SO42- release of 97 % was achieved with a 5 % concentration and the resulting leachate was further diluted to target a SO42- concentration of 12.4 g·L-1 for utilization with the isolated consortia. Compared to water leachate, a significantly higher reduction rate was registered (2 g·L-1 of SO42) using the IS consortium, demonstrating limited inhibition effect of sulfide- concentration on SRB functionalities. Moreover, metagenomic analysis of the consortia revealed that using PG as a source of SO42- increased the abundance of Deltaproteobacteria, including known SRB like Desulfovibrio, Desulfomicrobium, and Desulfosporosinus, as well as novel SRB genera (Cupidesulfovibrio, Desulfocurvus, Desulfococcus) that showed, for the first time, significant potential as novel sulfate-reducers using PG as a SO42- source.

Microbial transformations by sulfur bacteria can recover value from phosphogypsum: A global problem and a possible solution.

Rising global population and affluence are increasing demands for food production and the phosphorus (P) fertilizers needed to grow that food. Essential are new approaches for managing the growing amount of phosphogypsum (PG) that is a by-product of phosphoric-acid production from phosphate rock. Today, only ~15% of the worldwide production of PG is recycled, mainly for agriculture and road construction. This review addresses microbial valorization of PG through strategies that apply sulfur-transforming bacteria: sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). The focus is on recovering elemental sulfur (S0), which can be used to make the sulfuric acid needed to produce phosphoric acid from rock phosphate. Our review provides in-depth understanding of the microbiological, chemical, and technological bases for microbial reclamation of S0 from PG. The review presents the principles and practices for sulfate leaching from PG, reduction of sulfate to sulfide by SRB, and oxidation of sulfide to S0 by SOB. The choice of electron donor for SRB, control of oxygen delivery to SOB, and nutrient requirements are emphasized. Although microorganism-based technologies for PG reclamation are far from mature, the efficiency of such SRB- and SOB-based processes has been documented at laboratory and industrial scales. This review should spur biotechnological advances toward recovering value from PG.

High-throughput DNA sequencing reveals the dominance of pico- and other filamentous cyanobacteria in an urban freshwater Lake.

The current study presents findings related to algal blooms in a fresh water lake, which has been experiencing severe cyanobacterial blooms (CyanoHABs). Primarily, picocyanobacteria belonging to the genus Synechococcus and filamentous cyanobacterial group belonging to Aphanizomenon and Dolichospermum dominated top water column during non-bloom and bloom periods respectively. The dominance of Synechococcus in early summer informs that blooming in Utah Lake starts in early summer and then later is taken over by other bloom-forming cyanobacteria, such as species belonging to the genus Aphanizomenon. A strong negative correlation (r = -0.9, p < 0.001) was found between the occurrence of Aphanizomenon and Synechococcus which correlates very well with the fact that the blooms of these two different cyanobacteria never coexisted. The predominance of cyanobacteria in 2017 was attributed more to temperature (r = 0.18, p < 0.001). The Actinobacteria was negatively correlated with primary production and high chlorophyll a concentration. Flavobacterium and Limnohabitans were the main phytoplankton colonizers and predators detected that could secrete extracellular enzymes to degrade algal exudates (such as proteins and polysaccharides). Additionally, cyanotoxins producers Microcystis aeruginosa and Planktothrix accounted for up to 12.43% and 7.04% of total cyanobacteria abundance during blooms. The relative abundance of chloroplast reads was overall lower than the cyanobacteria reads, except for the May 5th sampling in 2017. There was inter-annual variability in the bloom-associated heterotrophic bacterial populations, but these populations were consistent with bloom-associated bacterial populations found in other lakes. Community diversity analysis for both Shannon and Simpson indices indicated lower community diversity during the bloom period. The beta diversity conducted by PCoA and UPGMA trees suggested the significant temporal rather than spatial impacts on shaping the phytoplankton community structures during the summer season.